Not able to play attached audio file in Messaging Application

Bug 5782423
When an mms draft is deleted, the code needs to clear its draft uri
variable. Otherwise when the code goes to update a draft, it will try to
update a draft that's not there, rather than creating a new draft.

Change-Id: I92f252aaac4524d693827395becb341f06c0828f
diff --git a/src/com/android/mms/data/WorkingMessage.java b/src/com/android/mms/data/WorkingMessage.java
index d84fbcd..c44b4ca 100755
--- a/src/com/android/mms/data/WorkingMessage.java
+++ b/src/com/android/mms/data/WorkingMessage.java
@@ -827,6 +827,7 @@
                 // user turns an mms back into a sms, such as creating an mms draft with a picture,
                 // then removing the picture.
                 asyncDeleteDraftMmsMessage(mConversation);
+                mMessageUri = null;
             }
         }
 
@@ -1597,6 +1598,7 @@
         values.put(Sms.TYPE, Sms.MESSAGE_TYPE_DRAFT);
         SqliteWrapper.insert(mActivity, mContentResolver, Sms.CONTENT_URI, values);
         asyncDeleteDraftMmsMessage(conv);
+        mMessageUri = null;
     }
 
     private void asyncDelete(final Uri uri, final String selection, final String[] selectionArgs) {